Most vehicles are made from a metal frame that serves as the main structure on which all other vehicle components or parts are mounted. In cars, the frame usually defines an opening from the passenger compartment toward a front of the vehicle. In assembly, a front windshield is mounted onto the frame so as to cover the opening. The upper end of the opening is usually marked by a so-called headliner frame element, or header for short. This header forms the front end of the vehicle's roof. Although moon roofs or other transparent roof panels are used on some vehicles, the rest of the roof is generally opaque. That is, the header forms a visual boundary such that the driver (or a front seat passenger) can only see out of the vehicle below the header.
Because the header is positioned immediately above the windshield it has become customary to mount certain vehicle components to this structure. For example, most cars have a driver side visor and a passenger side visor attached to the header. Each visor usually has a hinge attachment at one end and a clip attachment at the other end. Often, both the hinge and the clip are attached directly or indirectly to the header. The hinge, which is usually the outboard of the two attachments, typically allows the visor to be rotated to a position parallel with the side window to block light from the side.
Traditional visors can either be stowed, when they lie flat against the interior roof, or deployed, when they are flipped down to partially block out incoming light. While stowed, the visors are usually not considered a significant visual distraction, mainly because the stowed visor is simply covering a part of the interior roof that is not transparent anyway.